Ignition timing control system for internal combustion engines

ABSTRACT

To obtain optimum combustion of fuel in an internal combustion engine and prevent the occurrence of reverse torque therein, an ignition timing control system having a pulse generating circuit for generating first and second timing pulses corresponding to respective predetermined crank angles of the engine includes means for producing all essential signals and, hence, for setting maximum delay angle ignition timing, based on a reference which is the leading edge of the second timing signal, which edge is unaffected by unstable engine rotation as when the engine is started. To simplify and reduce circuitry, an ignition signal generating circuit and a reverse torque preventing circuit are integrated and adapted to perform both functions.

This is a division of application Ser. No. 790,512, filed Oct. 23, 1985.

BACKGROUND OF THE INVENTION

This invention relates to an ignition timing control system for internalcombustion engines.

An ignition timing control system of an internal combustion engine ingeneral is adapted to regulate the timing at which high-voltage pulsesare supplied to the engine spark plugs in dependence upon a change inengine rpm in order to achieve optimum combustion of fuel in the enginecylinders, and to prevent the occurrence of a reverse torque when theengine runs in a region of very low rpm.

An ignition timing control control system for an internal combustionengine includes a pulser for generating first and second timing pulses,which are positive and negative, respectively, at predetermined crankangle positions close to top dead center of an engine cylinder when theengine rotates. For reasons that will be described in detail later, themaximum delay angle position of ignition timing at low engine speedcorresponds to the trailing edge of the second timing pulse which isinfluenced by the rotational speed of the engine and becomes unstableparticularly when the engine is rotating at very low speed, as when theengine is started. With the conventional ignition timing control system,therefore, the maximum delay angle position for ignition timingcorresponds to the instant at which the second timing pulse decays and,hence, is influenced by the width of this pulse which, as mentionedabove, is affected by engine speed, especially in the low-speed region.As a result, ignition timing at the maximum delay angle can becomeunstable and it may be difficult to suppress the occurrence of reversetorque in the engine. This makes it necessary to increase the mechanicalstrength of the engine, which forms a cause of greater engine weight.

In another aspect of an internal combustion engine ignition system, acapacitative-discharge ignition unit (commonly referred to as a C.D.Iunit) is often employed in place of a mechanical breaker contact toprevent failures and deterioration in the overall ignition system. TheC.D.I. unit includes a generator (ACG) having a charging generator coil(hereafter referred to as an exciter coil) the output whereof charges acapacitor in an ignition circuit, and an ignition signal-forming coil(hereafter referred to as a pulser coil, which is wound on theabove-mentioned pulser) for producing an ignition signal applied to anignition signal generating circuit. The ignition signal generatingcircuit produces an ignition signal at a predetermined timing dependentupon the rotational speed of the engine, and the ignition signal turnson a thyristor (SCR) connected to the abovementioned capacitor todischarge the same. This causes a large current to flow into the primarycoil of an ignition coil connected to the capacitor, thereby producing ahigh voltage in the secondary coil of the ignition coil. The highvoltage causes a spark plug to produce a spark. Ignition timing in anarrangement of this type ordinarily is controlled by a phase differencebetween the aforementioned first (positive) and second (negative) timingpulse signals produced by the pulser coil.

A conventional ignition timing control system employing such a C.D.I.unit is designed to be free of the effects of power supply fluctuation,pulser gap variance and changes in temperature in order to achieveaccurate ignition timing and prevent the occurrence of reverse torque.However, this is achieved at the expense of circuit simplicity,compactness and ease of assembly, since a large number of circuitelements are required. There is thus room for improvement.

SUMMARY OF THE INVENTION

It is therefore a first object of the invention to provide an ignitiontiming control system for an internal combustion engine, having atwo-stage advance angle characteristic and in which ignition timing atlow engine rpm near the beginning of engine starting is controlled in aprecise manner to effectively suppress the occurrence of reverse torque,thereby enabling the weight of the engine to be reduced.

A second object of the invention is to provide an ignition timingcontrol system for an internal combustion engine, which is composed ofsimple circuitry and capable of being made small in size, and which islow in cost and designed to consume little electric power whileeffectively preventing reverse torque.

According to the present invention, the first object is attained byproviding an ignition timing control system for an internal combustionengine for applying a trigger signal to an ignition circuit which, inresponse to the trigger signal, applies a high-voltage pulse to anignition coil for driving a spark plug, the system comprising: pulsegenerating means for generating first and second timing pulsescorresponding to respective predetermined crank angle positions of theengine; a first sawtooth wave generating circuit responsive to thesecond timing pulse for generating a first sawtooth signal of apredetermined slope in synchronism with a leading edge of the secondtiming pulse; a second sawtooth wave generating circuit responsive tothe first and second timing pulses for generating a second sawtoothsignal which rises generally vertically at a leading edge of the firsttiming pulse, decays generally vertically at the leading edge of thesecond timing pulse, and rises between the leading edges of the firstand second timing pulses at a slope greater than the predetermined slopeof the first sawtooth signal; a third sawtooth wave generating circuitconnected to the first and second sawtooth wave generating circuits forgenerating a third sawtooth signal which rises at the leading edge ofthe first timing pulse at a slope greater than the predetermined slopeof the first sawtooth signal, and decays generally vertically at theleading edge of the second timing pulse; a rectangular wave generatingcircuit which compares the first and third sawtooth signals forproducing a rectangular wave signal of a level higher than that of thesecond sawtooth signal from an instant at which signal levels of thefirst and third sawtooth signals coincide until the leading edge of thesecond timing pulse; a comparator circuit which compares the firstsawtooth signal with one of the second sawtooth signal and rectangularwave signal for generating a drive signal when signal levels of the twocompared signals coincide; and a trigger signal generating circuit whichreceives the drive signal from the comparator circuit for generating thetrigger signal in response to the drive signal.

Thus, according to the first embodiment of the invention, the firstsawtooth signal is generated in synchronism with the leading edge of thesecond timing pulse, and the other signals likewise are formed so as todecay at the leading edge of the second timing pulse. The result is atwo-stage advance angle characteristic for coping with changes in enginespeed. Also, maximum delay angle ignition timing can be set based on theleading edge of the second timing pulse, which edge is not influenced byunstable rotation as when the engine is started. This makes possibleprecise control of ignition timing in order to effectively suppress thegeneration of reverse torque, thus enabling a reduction in engineweight.

According to the present invention, the second object is attained byproviding an ignition timing control system for an internal combustionengine, comprising: a pulse generating circuit for generating first andsecond pulse signals corresponding to respective predetermined crankangles of the engine; a rectangular wave generating circuit responsiveto the first and second pulse signals from the pulse generating circuitfor generating a rectangular wave signal which rises at a predeterminedslope from an instant of generation of the first pulse signal, and whichdecays at a slope less than the predetermined slope from an instant ofgeneration of the second pulse signal; a decision circuit responsive tothe rectangular wave signal from the rectangular wave generating circuitfor producing an output of logic level "0" when a signal level of therectangular wave signal is higher than a predetermined level, and anoutput of logic level "1" when the signal level is lower than thepredetermined level; a triangular wave generating circuit connected tothe decision circuit for generating a triangular signal which rises at aconstant and gentle slope from an instant the decision circuit producesthe output of logic level "1", decays at a slope defining apredetermined angle from an instant the first pulse signal is generated,and which then decays generally vertically to a logic level of "0" at aninstant the second pulse signal is generated; and an ignition signalgenerating circuit connected to the decision circuit and to thetriangular wave generating circuit for generating an ignition signalcommanding an igniting action when the decision circuit and triangularwave generating circuit both produce outputs of logic level "0".

Thus, according to the second embodiment of the invention, the ignitionsignal generating circuit is adapted to generate the ignition signal inresponse to a combination of binary signals from the decision circuitand triangular wave generating circuit. It is therefore possible toconstruct these circuits using logic circuitry. This enables ageneral-purpose IC to be used to increase mounting density, therebyreducing the size and weight and lowering the cost. Further, since suchcircuitry as the decision circuit may be constructed using a C-MOSgeneralpurpose logic IC, power consumption can be reduced and the powergenerated by the exciter coil can be used efficiently as the spark plugignition power.

Other features and advantages of the present invention will be apparentfrom the following description taken in conjunction with theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1a and 1b are schematic views illustrating the relationship betweencrank angle position and a pulser coil in an internal combustion engine:

FIG. 2 is a timing chart illustrating the operation of an ignitiontiming control system according to the prior art;

FIG. 3a -3e are schematic views illustrating the relationship betweencrank angle position and a pulser coil in an internal combustion engine;

FIG. 4 is a timing chart illustrating output signals produced by thepulser coil;

FIG. 5 is a circuit diagram illustrating an internal combustion engineignition timing control system according to the prior art;

FIG. 6 is a block diagram illustrating an ignition signal generatingcircuit of the prior-art system of FIG. 5 in the form of functionalblocks;

FIG. 7 is a timing chart illustrating the operation of the prior-artsystem of FIG. 5;

FIGS. 8, 9 and 10 are timing charts illustrating angle advance ofignition timing as performed by the prior-art system of FIG. 5;

FIG. 11 is a circuit diagram illustrating a first embodiment of aninternal combustion engine ignition timing control system according tothe present invention;

FIG. 12 is a timing chart illustrating the operation of the firstembodiment of FIG. 11;

FIG. 13 is a timing chart illustrating angle advance of ignition timingas performed by the first embodiment of FIG. 11;

FIG. 14 is a graph illustrating an advance angle characteristic ofignition timing with respect to engine rpm in the first embodiment ofFIG. 11;

FIG. 15 is a circuit diagram illustrating a second embodiment of aninternal combustion engine ignition timing control system according tothe present invention;

FIG. 16 is a timing chart illustrating the operation of the secondembodiment of FIG. 15;

FIG. 17 is a timing chart illustrating angle advance of ignition timingas performed by the second embodiment of FIG. 15;

FIG. 18 is a graph illustrating an advance angle characteristic ofignition timing with respect to engine rpm in the second embodiment ofFIG. 15; and

FIG. 19 is a timing chart useful in describing the prevention of reversetorque according to the second embodiment of FIG. 15.

DETAILED DESCRIPTION

Before turning to a detailed description of embodiments of the presentinvention, the problems encountered in the prior art will be discussedin greater detail with reference to FIGS. 1 through 10.

FIGS. 1 and 2 are useful in describing an internal combustion engineignition timing control system previously proposed by the assignee ofthe present application and disclosed in the specification of JapaneseProvisional Patent Publication (Kokai) No. 60-26174, published Feb. 9,1985. FIG. 1 illustrates pulse generating means, hereinafter referred toas a pulser, for generating first (positive) and second (negative)timing pulses Pc1, Pc2, respectively, at predetermined crank anglepositions close to top dead center of an engine cylinder (hereinafterreferred to as "TDC") when the engine rotates in the forward direction.The pulser includes a flywheel 12 mounted on an engine crankshaft 11, aninductor 13 made of a ferromagnetic material such as iron and fixedlysecured to the flywheel 12, a magnet 14 so arranged that the inductor 13will come into direct opposition therewith as the flywheel 12 rotates,and a pulser coil 1b wound on the magnet 14. The first timing pulse Pc1rises, as shown by the arrow 15a in (a) of FIG. 2, at an angularposition where one end 13a of the inductor 13 begins to pass by themagnet 14 with rotation of the crankshaft 11. The second timing pulsePc2 rises, as shown by the arrow 15b in (a) of FIG. 2, at an angularposition where the other end 13b of the inductor 13 departs from themagnet 14. The first and second timing pulses Pc1, Pc2 are thusgenerated at predetermined crank angle positions as the engine rotates.An interval 16 between the instants at which the first and second timingpulses Pc1, Pc2 rise is constant so long as the engine rpm remains thesame. Control circuitry in the aformentioned patent application includesa first sawtooth generating circuit for generating a first sawtoothsignal [(b) of FIG. 2] in synchronism with the trailing edge [arrow 15cin (a) of FIG. 2] of the second timing pulse Pc2, a second sawtoothgenerating circuit for generating a second sawtooth signal [(c) of FIG.2] which rises generally vertically at the leading edge of the firstpulse Pc1, and then gradually at a slope greater than that of the firstsawtooth signal, and which then decays generally vertically at thetrailing edge of the second pulse Pc2, a rectangular wave generatingcircuit for generating a rectangular wave signal [(d) of FIG. 2] of alevel higher than that of the second sawtooth signal during theoccurrence of the second timing pulse Pc2, a comparator circuit whichcompares the first sawtooth signal with the second sawtooth signal orwith the rectangular wave signal for producing an ON signal when thelevels of the two compared signals agree, and a trigger signalgenerating circuit for generating a trigger signal, which triggers anignition circuit, in response to the ON signal.

In the foregoing ignition timing control system, the trailing edge ofthe second timing pulse Pc2 at 15c in (a) of FIG. 2 serves as areference point on the basis of which the other signals are generated.Specifically, the first sawtooth signal is generated in synchronism withthis reference point, and the other signals are generated in such amanner that their trailing edges are timed to the above reference point,as depicted in (c), (d) and (e) of FIG. 2. Since the trailing edges ofthese signals are timed to the trailing edge of the second timing pulsePc2, the maximum delay angle position of ignition timing at low enginespeed corresponds to the moment at which the second timing pulse Pc2decays, i.e., to the trailing edge of the pulse Pc2. When the enginespeed rises, the comparator circuit responds by producing the ON signalat a position correspondingly advanced in order to advance the ignitiontiming by a required amount.

Though the instants 15a, 15b at which the respective first and secondtiming pulses Pc1, Pc2 generated by the pulser rise are determined by,e.g., the distance between the ends 13a, 13b of the inductor 13, thepulse widths of these pulses Pc1, Pc2 are influenced by the rotationalspeed of the engine and tends to develop instability particularly atvery low engine speeds that prevail when the engine is started.

Accordingly, with the foregoing ignition timing control system, themaximum delay angle position for ignition timing corresponds to theinstant at which the second timing pulse Pc2 decays and, hence, isinfluenced by the width of this pulse. Consequently, there are occasionswhere ignition timing at the maximum delay angle becomes unstable, anddifficulty is experienced in reliably suppressing the occurrence ofreverse torque in the engine. This makes it necessary to increase themechanical strength of the engine and results in greater engine weight.

The aformentioned is one of the problems the present invention seeks tosolve in a first embodiment thereof. Another drawback encountered in theprior art will now be described in detail with reference to FIGS. 3through 10.

A motorcycle engine generally is started by stepping down on a kicklever. If the stepping or kicking force applied by the rider is tooweak, however, the compressive force internally of the cylinder is notovercome and the piston does not surmount TDC. Instead, the piston isforced back by this compressive force, as a result of which the enginerotates in the reverse direction.

This reverse rotation of the engine can result in an explosion in thereverse direction. Specifically, at low crankshaft rpm, the piston isforced back before TDC (hereinafter referred to as "BTDC") by thecompression internally of the ccmbustion chamber and ignition takesplace when the crankshaft begins rotating in the reverse direction,thereby causing the explosion at reverse rotation. Alternatively, thepiston may be forced back BTDC by the pressure of an explosion whichoccurs after normal ignition. In the case of the former, the first pulsesignal Pc1 is produced [(b) of FIG. 4] when the inductor 13 passes theposition of (b) of FIG. 3, and after the inductor 13 then passes theposition of (c) of FIG. 3 and before it reaches the position of (d) ofthe figure, reverse rotation takes place, and the second pulse signalPc2 is produced [(b) of FIG. 4] when the inductor 13 again passes theposition of (b), whereupon ignition occurs. In the case of the latter,the second pulse signal Pc2 is produced [(c) of FIG. 4] to causeignition when the inductor 13 passes the position of (d) of FIG. 2, andthe piston is forced back by the pressure of an explosion before theinductor 13 reaches the position of (e) of FIG. 2. When the operation isnormal, the first and second timing pulses Pc1, Pc2 occur at a timeinterval ta, as illustrated in (a) of FIG. 4. The pulse signal waveformsof (b) and (c) of FIG. 4 resulting from reverse rotation respectivelyinvolve time intervals tb, tc between the first and second timing pulsesPc1, Pc2 that are long in comparison with the time interval ta.

When the piston is at a position near TDC as illustrated in FIG. 3 andthe mixture inside the cylinder explodes, a large reverse torque isgenerated. The reverse torque acts in a direction opposite to that ofthe torque applied at the kick lever, and both torques act upon thegears and bearings arranged between the kick lever and crankshaft andsubject the engine to excessive forces.

In an effort to eliminate the foregoing drawback, the applicant hasproposed an internal combustion engine ignition timing control circuitdisclosed in the specification of Japanese Patent Application No.59-116662, not published yet. As illustrated in FIG. 5, the circuitincludes a generator 1 having an exciter coil 1a and the aforementionedpulser coil 1b. The ungrounded end of the exciter coil 1a is connectedto an ignition circuit 2 for producing high-voltage energy. The ignitioncircuit 2 includes a diode Do for rectifying the output of the excitercoil 1a, a capacitor Co charged by the rectified output of the diode Do,and a thyristor SCR connected to the junction of the diode Do andcapacitor Co for controlling the discharge of the capacitor Co. Theoutput side of the capacitor Co, which serves as the output terminal ofthe ignition circuit 2, is connected to a primary coil 3a which, incombination with a secondary coil 3b, forms an ignition coil 3. Theungrounded side of the secondary coil 3b is connected to a spark plug 4.An ignition signal generating circuit 5, which serves as an advanceangle circuit, is arranged between the pulser coil 1b of the generator 1and the thyristor SCR of ignition circuit 2. The ignition signalgeneration circuit 5 is provided with an ignition control circuit 6,which serves to prevent reverse torque.

If considered in terms of function, the ignition signal generatingcircuit 5 comprises a number of circuit blocks, specifically a powersupply circuit 101 and, as illustrated also in FIG. 6, a second sawtoothsignal generating circuit 102 for converting the signal waveform fromthe pulser coil 1b into a second sawtooth signal signal Vb [(b) of FIG.7] delivered at an output terminal a, a first sawtooth signal generatingcircuit 103 for converting the signal waveform from pulser coil 1b intoa first sawtooth signal, signal Va [(b) of FIG. 7] delivered at anoutput terminal b, and a trigger signal generating circuit 104 having acomparator section 104' for comparing the voltage levels of the sawtoothsignals Va, Vb, the circuit 104 generating a trigger signal at itsoutput terminal c depending upon the output of the comparator section104'.

The specific construction and operation of the circuit blocks 101through 104 will now be described.

When the engine is started and the generator 1 begins rotating, theexciter coil 1a and pulser coil 1b each develop a voltage. The excitercoil 1a produces an output current which charges the capacitor Co inignition circuit 2. Concurrently, capacitors C1, C2 in the power supplycircuit 101 are charged to a voltage Ve regulated by a zener diode Dz1.The pulser coil 1b generates the first timing pulse Pc1, shown in (a) ofFIG. 7, in response to which a transistor Q4 in the second sawtoothsignal generating circuit 102 is driven into conduction, or turned on,thereby turning on a transistor Q1. As a result, a transistor Q2 isturned on so that a capacitor C4 is charged to the voltage at apotential dividing point 7 and a capacitor C3 is charged to a voltageapproximately equivalent to Ve. Since the voltage Ve to which thecapacitor C3 is charged is higher than that to which the capacitor C4 ischarged, the latter is charged to the voltage Ve at a predetermined timeconstant decided by the capacitor C3 and a resistor R8. As will bedescribed later, the capacitor C3 is discharged when the second timingpulse Pc2 is produced [(a) of FIG. 7] by the pulser coil 1b to turn ontransistors Q5, Q6. Owing to this charging and discharging of thecapacitor C3, the terminal voltage of capacitor C3, namely the secondsawtooth signal Vb, takes on the form of the sawtooth voltage having thevertically rising leading edge, as shown in (b) of FIG. 7. When enginerpm Ne changes from N1 to N4 (where N1<N2<N3<N4), as shown in (a) ofFIG. 7, the slope of second sawtooth signal Vb remains constant and onlythe peak value thereof changes, this becoming progressively smaller asengine rpm rises.

At the instant capacitor C3 is completely discharged by conduction ofthe transistor Q5, a capacitor C8 is charged at a time constant decidedby resistors R17, R18. The maximum voltage developed by capacitor C8,namely the first sawtooth signal Va, is a sawtooth voltage which, atmaximum, attains the voltage Ve, as shown in (c) of FIG. 7. Thecircuitry is so designed that the first sawtooth signal Va rises at aslower rate that the second sawtooth signal Vb. When engine rpm Ne risesfrom N1 to N4 (where N1<N2<N3<N4), as shown in FIG. 7, the slope offirst sawtooth signal Va remains constant and only the peak valuethereof changes, this becoming progressively smaller as engine rpmincreases.

The trigger signal generating circuit 104 operates when the secondtiming pulse Pc2 from the pulser coil 1b is produced, or when the levelof the second sawtooth signal Vb exceeds that of the first sawtoothsignal Va. Reference is now made to ignition for the case where thesecond timing pulse Pc2 is produced. At the instant the pulse Pc2arrives, the transistor Q5 is turned on and capacitor C8 beginsdischarging, whereupon the transistor Q6 is driven into conduction todischarge the capacitor C4 and, hence, the capacitor C3. Conduction ofthe transistor Q6 causes a transistor Q7 to turn on, and this in turndrives a transistor Q3 into conduction, thereby producing a triggersignal [(d) of FIG. 7] at a timing T1 to turn on the thyristor SCR. As aresult, the charge in capacitor Co is discharged through the thyristorSCR to produce a large current flow (namely a discharge current) intothe primary coil 3a of ignition coil 3. This in turn generates a highvoltage in the secondary coil 3b to ignite the spark plug 4. Theignition timing at this instant is the maximum delay angle. As theengine rpm successively rises to N2, N3 and then N4, the ignition timingin each instance is the moment at which the level of the first sawtoothsignal Va surpasses the level of the second sawtooth signal Vb, as shownin (d) of FIG. 7. When this occurs, the transistor Q6 is turned on andthe trigger signal is produced, as described above. At the engine rpm ofN2, the ignition signal is produced at a timing T2. At engine rpms of N3and N4, the trigger signal is produced at timings T3, T4, respectively,as shown in (d) of FIG. 7 (d). Thus, ignition timing is advanced fromthe maximum delay angle each time by an angle of a prescribed magnitude.Note that the ignition timing in accordance with the engine rpm of N4corresponds to the end of angle advance.

The ignition control circuit 6, which acts to prevent the occurrence ofreverse torque, will now be described with reference to FIGS. 8 through10. The ignition control circuit 6 is composed of three circuit blocks,namely a Vc signal generator 6a, a comparator 6b and an ignitioncontroller 6. The Vc signal generator 6a includes a capacitor C10charged by the power supply circuit 101 to a terminal voltageapproximately equal to the power supply voltage Ve. When the capacitorC3 is charged at the rise of the first timing pulse Pc1, a transistor Q8is turned on and the capacitor C10 begins discharging through thetransistor Q8 at a time constant decided by a resistor 25. When thetransistors Q5, Q6 are turned on at the trailing edge of the secondtiming pulse Pc2 to discharge the capacitor C3 and cause its terminalvoltage to drop, the transistor Q8 is cut off. As a result, thecapacitor C10 stops discharging and simultaneously begins charging againat a time constant decided by a resistor R26. This produces the signalVc having the waveform shown in (b) of FIG. 8. The comparator 6bcompares the level of this signal with a voltage Vd at a potentialdividing point d. When the condition Vc>Vd holds (which lasts for afixed period of time serving as a reference time tz), a transistor Q9 inthe comparator 6b conducts. A transistor Q10 in the ignition controller6c is therefore turned on as long as the transistor Q9 remainsconductive, as a result of which the collector voltage of transistor Q10varies as shown in (c) of FIG. 8. A transistor Q11 in the ignitioncontroller 6c has its base connected to the collector of transistor Q10and is conductive as long as the transistor Q10 is cut off, during whichtime the gate terminal of the thyristor SCR is grounded. Accordingly, asshown in (a) and (b) of FIG. 9, when the second timing pulse Pc2 isapplied before the lapse of the time period tz, which is measured fromthe instant at which the first timing pulse Pc1 rises, and an ignitionpulse Pt is produced at the leading edge of the second timing pulse Pc2[(d) of FIG. 9], the thyristor SCR is turned on and the spark plug 4produces a spark. However, as shown in (a) and (b) of FIG. 10, thethyristor SCR cannot turn on and the spark plug 4 will not spark if theignition pulse Pt is produced at the trailing edge of the second timingpulse Pc2 applied after passage of the time tz counting from the leadingedge of the first timing pulse Pc1. Thus, a reverse torque is preventedfrom occurring.

Thus, the ignition timing control circuit for internal combustionengines according to the previously proposed application is advantageousin that it eliminates the influence of power supply fluctuation, pulsergap variance and temperature change to achieve accurate ignition timingand prevent the occurrence of reverse torque.

The drawback encountered in the above circuit is the large number ofcomponent parts required. For example, the second sawtooth signalgenerating circuit 102 in the ignition signal generating circuit 5includes numerous discrete electrical parts such as three transistors,nine resistors, three capacitors, and one diode; the first sawtoothsignal generating circuit 103 includes discrete parts such as onetransistor, three resistors, two capacitors and one diode; and theignition timing determination circuit 104 includes three transistors,seven resistors and one capacitor. Moreover, it is required to providethe ignition control circuit 6, which includes the Vc signal generator6a, the comparator 6b and the ignition controller 6c. The large numberof circuit elements necessitates considerable labor for assembly andplaces a limitation upon the size reduction that can be obtained. Thisis another problem addressed by the present invention in a secondembodiment thereof.

The first embodiment of the present invention will now be described withreference to FIGS. 11 through 14.

The generator 1, ignition circuit 2, ignition coil 3 and spark plug 4are constructed, interconnected and operate in the manner describedabove and need not be described again in detail. In the presentembodiment, the ignition timing control circuitry arranged between thepulser coil 1b and ignition circuit 2 include the power supply circuit101, the first sawtooth generating circuit 103 for generating the firstsawtooth signal Va [(b) of FIG. 12] in synchronism with the leading edgeof the second timing pulse Pc2, the second sawtooth generating circuit102 for generating the second sawtooth signal Vb [(c) of FIG. 12] whichrises rapidly or generally vertically at the leading edge of the firsttiming pulse Pc1, gradually at a slope greater than that of the firstsawtooth signal, and which then decays rapidly or generally verticallyat the leading edge of the second timing pulse Pc2, a third sawtoothsignal generating circuit 105 for generating a third sawtooth signal Vc'[(d) of FIG. 12] which rises gradually at the leading edge of the firsttiming pulse Pc1 at a slope greater than that of the first sawtoothsignal and then decays rapidly or generally vertically at the leadingedge of the second timing pulse Pc2, a rectangular wave generatingcircuit 106 which compares the levels of the first and third sawtoothwave signals Va, Vc' for producing a rectangular wave signal Vd [(e) ofFIG. 12] of a level higher than that of the second sawtooth signal Vbfrom the moment at which the sawtooth wave signals Va, Vc' coincideuntil the leading edge of the second timing pulse Pc2, a comparatorcircuit 107 for comparing the first sawtooth signal Va with a signal Vf[(f) of FIG. 12], which is the resultant of the second sawtooth signalVb and the rectangular wave signal Vd, and for generating a drive signalwhen the levels of the signals Va, Vf agree, and the trigger signalgenerating circuit 104 for generating the trigger signal, which drivesthe ignition circuit 2, in response to the drive signal from thecomparator circuit 107.

The power supply circuit 101 comprises a diode D1 for rectifying the ACvoltage developed by the exciter coil 1a, the capacitor C2 charged bythe rectified output through a resistor R1, a diode D2 and the zenerdiode Dz1. The diodes D2, Dz1 are for regulating the charging voltage toa voltage Ve of a predetermined level.

The first sawtooth generating circuit 103 includes the capacitor C8,which is connected to the power supply circuit 101 through the resistorR17, and the transistor Q5 whose base is connected to the ungrounded endof the capacitor C8 through a resistor R16. The transistor Q5 is turnedon by the leading edge of the second (negative) timing pulse Pc2, uponwhich a discharge circuit is formed by resistors R14, R16 to dischargethe voltage charged in the capacitor C8. The base of transistor Q5 isconnected to ground through a parallel circuit composed of a biassetting resistor R15 and a capacitor C7. A diode D6 connected betweenground and one end of resistor R16 is for waveshaping and otherpurposes.

The second sawtooth generating circuit 102 includes a power supply line50 connected at one end to the power supply circuit 1 and at the otherend to a capacitor C3 through a transistor Q1, a resistor R4 and aforwardly connected diode D5. The other end of the capacitor C3 isconnected to ground. The base of transistor Q1 is connected to groundthrough a resistor R3 and a transistor Q4, and the base of transistor Q4is connected to an output terminal a' of the pulser coil 1b through aparallel circuit composed of a resistor R13 and a capacitor C5, and aresistor R12. A series circuit comprising a transistor Q2 and acapacitor C4 is connected between the power supply line 50 and ground,with the collector of transistor Q2 connected to the collector oftransistor Q1 through the resistor R4. Arranged in parallel with thetransistor Q2 and the capacitor C4 is a voltage dividing circuitcomposed of two serially connected resistors R5, R6. The voltagedividing circuit has a voltage dividing point 7 connected to the base oftransistor Q2. The junction c' between the transistor Q2 and thecapacitor C4 is connected to the ungrounded side of the capacitor C3through a resistor R8.

The third sawtooth wave generating circuit 106 includes a capacitor C17,one end of which is grounded, and the other end is connected via aresistor R34 to the ungrounded side of the capacitor C3 in the secondsawtooth generating circuit 102. Connected in parallel with the resistorR34 is a diode D15 arranged forwardly from the side of capacitor C17 tothe side of capacitor C3.

The rectangular wave generating circuit 106 includes a comparator 70 anda transistor Q12. The comparator 70 has a non-inverting input terminal70a which receives the signal voltage of the first sawtooth signal Vaset to an appropriate level by two resistors R35, R36, and an invertinginput terminal 70b to which is connected an output terminal d' of thethird sawtooth generating circuit 105. The comparator 70 also has anoutput terminal connected to the base of a transistor Q12 through aresistor R37. The emitter of transistor Q12 is connected to theungrounded side of the capacitor C3 in the second sawtooth generatingcircuit 102, and the collector thereof is connected to an outputterminal e through a resistor R39.

The comparator circuit 107 includes a transistor Q6' whose base isconnected to the output terminal b of first sawtooth generating circuit103 through a resistor 19', and whose emitter is connected to a commonjunction f between the output terminal c' of the second sawtoothgenerating circuit 102 and the output terminal e of the rectangular wavegenerating circuit 106, this junction serving as an output terminal forthe resultant waveform shown in (f) of FIG. 12. The collector oftransistor Q6' serves as an output terminal g for the drive signalproduced as the result of the comparison operation.

The trigger signal generating circuit 104 includes the two transistorsQ3, Q7. The power supply line 50 of the second sawtooth generatingcircuit 102 is connected to the emitter of transistor Q3 through theforwardly connected diode D5. The collector of transistor Q3 isconnected to the gate of the thyristor SCR in the ignition circuit 2through a potential dividing circuit composed of resistors R10, R11. Thebase of transistor Q3 is connected to ground via a resistor R22 and thetransistor Q7. The base of the latter is connected to the outputterminal g of comparator circuit 107 through a resistor R20. A resistorR21 connected between ground and the junction of resistor R20 and thebase of transistor Q7 is for setting the biasing voltage of thetransistor Q7.

The operation of the first embodiment will now be described withreference to FIGS. 11 through 14.

When the engine is started and the generator 1 begins rotating, theexciter coil 1a and pulser coil 1b each develop a voltage. The excitercoil 1a produces an AC output which is rectified by the diode Do of theignition circuit 2 to charge the capacitor Co. Concurrently, thecapacitor C2 of the power supply circuit 101 is charged under theregulation of zener diode Dz1 to the potential Ve.

The capacitor C8 in the first sawtooth generating circuit 103 is chargedby the voltage Ve of power supply circuit 101 in accordance with a timeconstant decided by the capacitor C8 and resistor R17. Next, when thepulser coil 1b produces the second (negative) timing pulse Pc2, thetransistor Q5 is turned on in synchronism with the leading edge of thesecond timing pulse Pc2 so that the voltage charged in capacitor C8 isdischarged through a path comprising discharge resistor R16, transistorQ5 and resistor R14, whereby the first sawtooth waveform Va shown in (b)of FIG. 12 is generated at the output terminal b of the first sawtoothgenerating circuit 103. The slope of the first sawtooth signal Va, whichis regulated at the time constant determined by resistor R17 andcapacitor C8, is constant. The first sawtooth signal Va has a pulseduration t1 regulated by generation of the second timing pulse Pc2.Thus, the signal waveform of the first sawtooth signal is synchronizedto the leading edge 15b of the second timing pulse Pc2. Therefore, asthe engine speed rises from N1 to N4 (N1<N2<N3<N4), the period at whichthe second timing pulse Pc2 is generated grows correspondingly shorter,in response to which the pulse duration t1 of the first sawtooth signalVa shortens, as from t1 to t1' and t1' to t2', as illustrated in FIG.13, so that the peak value of the first sawtooth signal Va graduallydiminishes.

When the pulser coil 1b produces the first (positive) timing pulse Pc1,the transistors Q4, Q1 in the second sawtooth generating circuit 102 areturned on, as a result of which the capacitor C3 is charged toapproximately the power supply voltage Ve. Conduction of transistor Q1causes the transistor Q2 to turn on, so that the capacitor C4 is chargedto the potential at the potential dividing point 7. Since the capacitorC3 is charged to a higher potential than the capacitor C4, the latter ischarged by the charging voltage of capacitor C3 at a predetermined timeconstant decided by the resistor R8. As mentioned earlier, the voltagecharged in capacitor C4 is discharged when the second pulse signal Pc2is produced by the pulser coil 1b, thereby turning on transistors Q1,Q6'. Accordingly, the second sawtooth signal Vb having the rapidly orgenerally vertically rising leading edge shown in (c) of FIG. 12 isgenerated at the output terminal c' of the second sawtooth generatingcircuit 102. The slope of the second sawtooth signal Vb is set by a timeconstant decided by the resistor R8, etc. so as to be greater than theslope of the first sawtooth signal Va. The second sawtooth signal Vb hasa pulse width t2 regulated by the interval (from 15a to 15b) between theleading edges of the first and second timing pulses Pc1, Pc2. As shownin FIG. 13, t2 grows successively smaller as engine rpm rises.Accordingly, the peak value of the second sawtooth signal Vb graduallydiminishes with an increase in engine rpm.

At the instant the transistor Q1 is turned on, the capacitor C17 in thethird sawtooth generating circuit 105 begins charging at a time constantregulated by the resistor R34 in combination with the capacitor C17. Ina manner similar to that described above, the charging of capacitor C17continues, due to the voltage accumulated in the capacitor C3, evenafter the transistor Q1 is cut off by extinguishment of the first timingpulse Pc1. The capacitor C17 is discharged when the transistors Q5, Q6'are turned on by the second timing pulse Pc2. Accordingly, the thirdsawtooth signal Vc' shown in (d) of FIG. 12 is generated at the outputterminal d'.

The comparator 70 in the rectangular wave generating circuit 106compares the signal level of the first sawtooth signal Va from theoutput terminal b and the signal level of the third sawtooth signal Vc'from the output terminal d', and produces an output of logical "0" whenthe signal level of Vc' surpasses that of Va. The "0" level outputcauses the transistor Q6' to conduct, thereby producing, at the outputterminal e, a rectangular wave signal Vd the pulse width whereofcorresponds to the period of time for which the transistor Q6' isconductive. Accordingly, a signal Vf shown in (f) of FIG. 12, which isthe resultant of the second sawtooth signal Vb and rectangular wavesignal Vd, is generated at the junction f at the common connectionbetween output terminals c' and e.

The trigger signal generating circuit 104 sends a trigger signal to theignition circuit 2 when the second timing pulse Pc2 from the pulser coil1b is produced, or when the comparator 107 issues the drive signal inresponse to the signal level of the resultant signal Vf exceeding thatof the first sawtooth signal Va. First, generation of the trigger signalwhere the second timing pulse Pc2 is produced will now be explained.

The transistor Q5 is turned on by the leading edge of the second timingpulse Pc2 and capacitor C8 begins discharging, whereupon the transistorQ6' is driven into conduction to discharge the capacitor C4 and, hence,the capacitor C3. Conduction of the transistor Q6' causes thetransistors Q7, Q3 to turn on, thereby producing the trigger signal toturn on the thyristor SCR. As a result, the charge in capacitor Co isdischarged through the thyristor SCR to produce a large dischargecurrent flow into the primary coil 3a of ignition coil 3. This in turncauses generation of a high voltage in the secondary coil 3b to causeignition of the spark plug 4. The ignition timing at this instant is themaximum delay angle, indicated at 8a in FIG. 14. The ignition timing ofthe maximum delay angle is thus regulated by the leading edge of thesecond timing pulse Pc2.

As the engine rpm successively rises from N2 at idling to N3 foradvancing the injection timing and then to N4 at high engine speed, theignition timing in each instance is the moment at which the signal levelof the resultant signal Vf surpasses the level of the first sawtoothsignal Va, these signal levels being compared by the comparator circuit107. When this occurs, the comparator circuit 107 sends the drive signalto the transistor Q7, which is turned on. This is immediately followedby conduction of the transistor Q3, whereby the spark plug is caused tospark as set forth above. As shown in 8b in FIG. 14, the ignition timingat this instant is held at a value corresponding to a constant low crankangle position in the region of engine speed N2 (idling) due to therelationship between the signal waveform of the resultant signal Vf andthe signal waveform of the first sawtooth signal Va. When the enginespeed N3 is attained (i.e., at or above which the injection timing is tobe advanced), the gradually rising portion of the resultant signal Vfcrosses the first sawtooth signal Va, so that the ignition timing isgradually advanced as engine rpm rises, as illustrated at 8c in FIG. 14.When the region of high engine speed N4 is attained, the ignition timingis held at a value corresponding to a constant high crank angleposition, as shown at 8d in FIG. 14. This provides a two-stage advanceangle characteristic for the ignition timing.

According to the first embodiment of the present invention, thetwo-stage advance angle characteristic makes it possible to achieveoptimum combustion in the engine cylinders in conformance with changesin engine speed. Moreover, maximum delay angle ignition timing can beset based on a reference which is the leading edge of the second timingpulse Pc2, this edge of the pulse being unaffected by unstable rotationof the engine as when the engine is started. Maximum delay angleignition timing therefore can be controlled in a precise manner toeffectively suppress the generation of reverse torque. Accordingly, theengine strength need not be raised to an unnecessary degree, thusenabling a reduction in the engine weight.

Reference is now made to FIGS. 15 through 19 to describe the secondembodiment of the ignition timing control system according to thepresent invention, in which the ignition timing generating circuit(advance angle circuit) 5 and ignition control circuit (reverse torqueprevention circuit) 6 appearing in FIG. 5 are included in integratedform to simplify the circuitry and reduce the hardware.

As shown in FIG. 15, the ignition timing control system according to thesecond embodiment includes a power supply circuit 101, a pulsegenerating circuit 108 for generating first and second pulse signalseach of which corresponds to a predetermined crank angle of the enginecrankshaft, a rectangular wave generating circuit 109 for generating arectangular wave which rises at a predetermined slope from an instant ofgeneration of the first pulse signal, and which decays at a gentlerslope from an instant of generation of the second pulse signal, adecision circuit 110 for producing an output of logic level "0" when thevoltage level of the rectangular wave signal is higher than apredetermined level, a triangular wave generating circuit 111 forgenerating a triangular signal which rises at a constant, gentle slopefrom an instant the decision circuit 110 produces an output of logiclevel "1", decays at a predetermined angle from an instant the firstpulse signal is generated, and which then reverts to the "0" level atthe instant the second pulse signal is generated, and an ignition signalgenerating circuit 112 for generating an ignition signal upon receiving"0" level signals from the decision circuit 110 and triangular wavegenerating circuit 111.

The pulse generating circuit 108 includes diodes D8, D9 connected inmutually opposing directions to the pulser coil 1b through the resistorR12. A parallel circuit composed of the resistor R14 and a bidirectionalzener diode Dz2 is connected between ground and the line interconnectingthe diodes D8, D9. The diodes D8, D9 produce the first (positive) andsecond (negative) pulse signals, which are applied to the rectangularwave generating circuit 109. The diode Dz2 is for protecting the circuitfrom excessive pulse voltages produced by the pulser coil 1b.

The rectangular wave generating circuit 109 includes a first inverter 9ahaving an input terminal connected to the conjunction between a resistorR32 and a transistor Q4 constituting a series circuit arranged between apower supply line 8 and ground. The base of transistor Q4 is connectedto a diode D8 of the pulse generating circuit 108 through a parallelcircuit composed of a resistor 13 and a capacitor C5, which is forpreventing noise. Forwardly connected to the output terminal of theinverter 9a is a diode D10. A capacitor C11 and a resistor R33 areconnected in parallel between ground and the output line of diode D10,which line is connected to ground through a resistor R40, a forwardlyconnected diode D11, and a reversely connected diode D12. The junctionbetween the diodes D11, D12 is connected to the diode D9 in the pulsegenerating circuit 108 through the transistor Q5.

The decision circuit 110 includes a second inverter 9b having an inputterminal to which the output line of diode D10 in the rectangular wavegenerating circuit 109 is connected. The inverter 9b has an internaltransistor switching element whose inversion threshold level Eth(approximately 0.7 V) is predetermined for operation of the inverter 9b.

The triangular wave generating circuit 111 includes a series circuitcomposed of a reversely connected diode D13, a resistor R41 and acapacitor C18 arranged between ground and the output line of the secondinverter 9b. A resistor R42 is connected in parallel with the seriallyconnected diode D13 and resistor R41. The ungrounded side of capacitorC18 is connected to the junction between diodes D11, D12 of therectangular wave generating circuit 109 through a forwardly connecteddiode D14.

The ignition signal generating circuit 112 includes a NAND circuit 10.The NAND circuit 10 has two input terminals, one of which is connectedto the output terminal of the second inverter 9b, the other of which isconnected to the ungrounded side of the capacitor C18 in the triangularwave generating circuit 111. The output terminal of NAND circuit 10 isconnected to the gate terminal of the thyristor SCR through a low-passfilter composed of a resistor R43 and a capacitor C12.

The operation of the second embodiment shown in FIG. 15 will now bedescribed with reference to FIGS. 16 through 19.

When the engine is started and the generator 1 begins rotating, theexciter coil 1a and pulser coil 1b each develop a voltage. The excitercoil 1a produces an output current which charges the capacitor Co in theignition circuit 2. Concurrently, the capacitor C2 in the power supplycircuit 101 is charged to a voltage regulated by the zener diode Dz1.When the pulser coil 1b applies the first timing pulse Pc1 to the pulsegenerating circuit 108 [(a) of FIG. 16], the diode D8 applies the signalas the first pulse signal to the transistor Q4, in response to which thetransistor Q4 is driven into conduction to change the input level of thefirst inverter 9a to ground potential, whereby the output terminal ofinverter 9a goes to logical "1". Owing to this "1" level output, thecapacitor C11 charges. The charged voltage thereafter dischargesgradually through the resistor R33 [(b) of FIG. 16]. Next, when thepulser coil 1b applies the second timing pulse Pc2 to the pulsegenerating circuit 108 [(a) of FIG. 16], the diode D9 applies the signalas the second pulse signal to the transistor Q5 in the rectangular wavegenerating circuit 109, thereby turning the transistor Q5 on. Inresponse thereto, the voltage charged in the capacitor C11 is dischargedat a slope gentler than that which prevailed during the voltage rise[(b) of FIG. 16], this being regulated by a discharge time constantdecided by such circuit elements as resistors R40 and R14. Accordingly,the rectangular wave generating circuit 109 generates the rectangularsignal Vg indicated at (b) in FIG. 16.

As mentioned above, the operating level of the second inverter 9b is setat a predetermined threshold value Eth. The decision circuit 110produces the output signal Vh of logic level "0" during the time thatthe level of the rectangular wave signal Vg exceeds the predeterminedthreshold level Eth of the inverter 9b, and produces the output signalof logic level "1" during the time that the level of the rectangularwave signal Vg is below the predetermined threshold level, as a bilevelsignal Vh shown in (c) of FIG. 16. When the rectangular wave signal Vgdecays at a gentle slope in response to generation of the second timingpulse Pc2 and falls below the predetermined level Eth, the secondinverter 9b produces the "1" level output as the bilevel signal Vh. Theleading edge of this "1" level pulse therefore occurs at a timingslightly later than that at which the second timing pulse Pc2 isgenerated, as shown in FIG. 16. At the instant the output of the secondinverter 9b rises from "0" to "1", the capacitor C18 in the triangularwave generator 111 begins charging at an gentle slope in accordance witha charging time constant decided by resistor R42 and the capacitance ofcapacitor C18 [(d) of FIG. 16]. Then, at the instant the output ofsecond inverter 9b reverts to the "0" level (i.e., when the first timingpulse Pc1 is generated), the voltage charged in capacitor C18 decays,i.e., discharges, at a fixed slope in accordance with a discharge timeconstant decided by such circuitry as the parallel circuit composed ofresistors R41 and R42 [(d) of FIG. 16]. When the second timing pulse Pc2is generated during the decay of this voltage signal, transistor Q5 isturned on. At the moment this occurs, capacitor C18 discharges rapidlyto the "0" level. Thus, a triangular wave signal Vi shown in (d) of FIG.16 is applied to the ignition signal generating circuit 112 from theungrounded side or point a of the capacitor C18 in the triangular wavegenerating circuit 111. As mentioned above, the timing at which theoutput Vh of second inverter 9b rises to the "1" level occurs slightlylater than that at which the second timing pulse Pc2 is generated, andthe potential or signal Vi at the ungrounded side of capacitor C18reverts to the "0" level at the moment the second timing pulse Pc2 isgenerated. Therefore, the two input signals of level "0" to the NANDcircuit 10 cause the circuit to produce "1" level output as an ignitionsignal Vj in synchronism with the generation of the second timing pulsePc2, as the result of which the ignition signal generating circuit 112delivers the ignition signal as shown in (e) of FIG. 16. This signalturns on the thyristor SCR so that the spark plug 4 is caused to sparkby the ignition coil 3. Since the illustrated example is applied whenthe engine is in a low speed region, the ignition timing at this instantcorresponds to the maximum delay angle.

Now will be explained angle advance of ignition timing with an increasein the engine speed, as well as the prevention of reverse torque.

As the engine speed rises, the time interval between generation of thefirst and second timing pulses Pc1, Pc2 shortens, and so does thecharging time interval of the capacitor C18 in the triangular wavegenerating circuit 111. As a result, the pulse width of the triangularwave signal Vi gradually diminishes, as indicated at (a) through (e) inFIG. 17. Since the charging time is long at low engine speed, the signallevel of the triangular wave signal Vi is sufficiently higher than theoperating or threshold level Eth' of the NAND circuit 10. Therefore, theinstant at which the triangular wave signal Vi decays sharply responsiveto the generation of the second timing pulse Pc2 corresponds to thetiming at which the thyristor SCR is turned on [(a) and (b) in FIG.17)]. As the peak level of the triangular wave signal Vi falls owing tothe shorter charging time interval of capacitor C18 caused by a rise inengine rpm, the intersection between the triangular wave signal and theoperating level Eth' of NAND gate 10 is gradually shifted leftward asshown in (a) through (e) of FIG. 17, so that the ignition timing has itsangle advanced in accordance with this leftward shift of theintersection point from (a) to (e) in FIG. 17 on the condition that therectangular wave signal in the rectangular wave generating circuit 109exceeds the threshold level Eth of the second inverter 9b. When enginerpm rises still higher so that the peak level of the triangular wavesignal Vi drops below the operating level Eth' of the NAND circuit 10,as shown in (e) of FIG. 17, one input terminal to the NAND circuit 10goes to the "0" level and stays there. Accordingly, the point at whichthe output Vh [(c) of FIG. 16] of the second inverter 9b decayscorresponds to the timing at which the thyristor SCR is turned on. Theignition timing at this instant is the maximum advance angle.

FIG. 18 is a characteristic illustrating angle advance of ignitiontiming as performed above. This shows that, as engine rpm rises, theignition timing is gradually advanced from the beginning j[corresponding to (b) in FIG. 17] of the advance operation and becomesconstant at the maximum advance angle following the end k [correspondingto (d) in FIG. 17] of the advance operation.

As for prevention of reverse torque, the rectangular wave signal Vgshown in (b) of FIG. 16 always decays gently owing to the dischargethrough the resistor R33 when the engine speed is very low. Therectangular wave signal Vg therefore drops below the threshold level Ethof the second inverter 9b before the second timing pulse PC2 isgenerated, as shown in (a) and (b) of FIG. 19. Accordingly, at theinstant the second timing pulse Pc2 is generated, the output Vh ofsecond inverter 9b will always be at the "1" level, so that thethyristor SCR cannot be turned on. This prevents ignition, which forms acause of reverse torque when the rider steps down on the kick lever.

According to the second embodiment of the present invention, thedecision circuit 110 and ignition signal generating circuit 112 operateon the basis of the binary signals "0" and "1", enabling the applicationof logic circuitry. Accordingly, a general-purpose IC can be used toheighten the mounting density, thereby reducing the size and weight andlowering the manufacturing cost. Furthermore, the ignition controlcircuit for preventing reverse torque need not be provided separately ofthe ignition signal generating circuit 112 for angle advance. Instead,the two circuits are integrated into a single circuit for implementingboth angle advance and the prevention of reverse torque. This makes itpossible to achieve an even greater reduction in size, weight and cost.In addition, since such circuitry as the decision circuit 110 is capableof employing a C-MOS general-purpose logic IC, the power consumption canbe reduced and the power generated by the exciter coil 3 can be usedefficiently as the spark plug ignition power.

As many apparently widely different embodiments of the present inventioncan be made without departing from the spirit and scope thereof, it isto be understood that the invention is not limited to the specificembodiments thereof except as defined in the appended claims.

What is claimed is:
 1. An ignition timing control system for an internalcombustion engine, comprising:a pulse generating circuit for generatingfirst and second pulse signals corresponding to respective predeterminedcrank angles of the internal combustion engine; a rectangular wavegenerating circuit which receives the first and second pulse signalsfrom said pulse generating circuit for generating a rectangular wavesignal which rises at a predetermined slope from an instant ofgeneration of the first pulse signal, and which decays at slope lessthan said predetermined slope from an instant of generation of thesecond pulse signal; a decision circuit which receives the rectangularwave signal from said rectangular wave generating circuit for producingan output of logic level "0" when a signal level of the rectangular wavesignal is higher than a predetermined level, and an output of logiclevel "1" when said signal level is lower than said predetermined level;a triangular wave generating circuit connected to said decision circuitfor generating a triangular signal which rises at a constant and gentleslope from an instant said decision circuit produces the output of logiclevel "1", decays at a slope defining a predetermined angle from aninstant the first pulse signal is generated, and which then decaysgenerally vertically to a logic level of "0" at an instant the secondpulse signal is generated; and an ignition signal generating circuitconnected to said decision circuit and to said triangular wavegenerating circuit for generating an ignition signal when said decisioncircuit and triangular wave generating circuit both produce outputs oflogic level "0".